This invention is particularly adaptable to an airfoil or blade which is useful for a helicopter, gyrocopter, or like aircraft where there is an airfoil or blade that orbits an axis on the aircraft. Further, this invention is applicable to airfoils which are supported on the aircraft and are in fact disposed only at a distance from the body or fuselage for orbiting same. In those aircraft, there is a foreshortened airfoil or blade, such as shown in U.S. Pat. No. 2,996,121 to Stub, as compared to the usual helicopter blade which has an extent from the fuselage to the radially outer tip of the blade.
Therefore, the airfoil span, which is its length along the orbiting radius, is short compared to the airfoil chord, which is its depth transverse to the span. As with the Stub arrangement, the airfoil of this invention is supported on cables which extend from the body or fuselage and thereby position the airfoil in response to centrifugal force acting on the orbiting airfoil. In that environment, the airfoil creates vortices, which are air currents moving from underneath the airfoil to above the air foil, and those vortices impede the air lift otherwise available to the airfoil because the air pressure is increased above the airfoil and decreased beneath the air foil because of the vortices.
The present invention overcomes the aforementioned problem and it does so in an efficient and economical manner in an aircraft which produces both vertical and forward flight. In this regard, the airfoil of this invention has a relatively low aspect ratio, that is, the ratio of the span to the chord, and the vortices problem is overcome by the application of shields or baffles at the radially inner and outer ends of the airfoil.
Another object of this invention is to provide an aircraft which is efficient in flight but employs only a minimum of material, such as wing or airfoil material, and has only a minimum weight, and occupies only a minimum space when not in flight.
With an airfoil having a low aspect ratio, as in this invention, the air currents at the ends of the airfoil are very significant and thus there is concern about the vortex at the airfoil ends. The orbiting airfoil inherently generates vortices which cause the air pressure to lessen below the airfoil and to increase above the airfoil, thus impeding the air lift desired. The lift varies according to the square of the velocity of the air passing over and under the airfoil. The speed of the radially outer tip of an airfoil is the fastest linear speed of the airfoil. Thus a very large lift can be generated at the tips of rotors or airfoils, and especially so when the vortex is negated, as in this invention.